Q: imessage not activated on iPhone 6s

I decided to swap my old 5c to 6s

everything went smoothly except iMessage which for some reason is not activated

- sim card is the same

- sim card works in both phones

- sim card does activate iMessage in 5c anytime

- new phone was activated successfully and its not simlocked

- i did log off/log in into iMessage in 6s

- i did full wipe

- i have removed all devices from iMessage

- i have registered iMessage again

- disabled iMessage with airplane mode + wifi on - also waiting for activation

- enabling GSM did not change anything despite message that carrier can charge for SMS (standard message)

- i have removed 5c from iCloud

- after couple of hours "iMessage cannot be activated"

- my carrier does not block any text messages - NOTE same sim card activates iMessage on 5c

can you explain me what is wrong here? i am out of ideas